1. Field of the Invention
The invention relates to dynamoelectric machine bearing lubrication systems and in particular to self-contained supplemental lubrication systems for oil ring lubricated hydrodynamic bearings utilized in induction motors.
2. Description of the Prior Art
Electrodynamic machines, such as horizontal shaft induction motors, have rotating shafts restrained by rolling element, hydrodynamic or hydrostatic bearings. Hydrodynamic bearings generate a self-sustaining pressurized lubricant liquid film interface between the bearing surface and the corresponding shaft journal. Lubricant forming the lubricant film needs to be refreshed to replace that which is inevitably squeezed out of the bearing/journal interface due to their relative rotation. Oil replenishment also conveniently transfers heat generated within the interface or by thermal gradient transfer between the surfaces away from the bearing, for example to a sump. For brevity, lubricant will hereafter be referred to as oil, as it is a commonly used industrial lubricant.
It is known and common in the induction motor arts to employ oil ring lubricated hydrodynamic bearings to support and constrain the rotating shaft. The hydrodynamic bearings are often contained in a bearing block portion of a bearing housing mounted on both axial ends of the motor. The bearing housing in cooperation with the motor housing forms an oil sump having a maximum fluid fill level below the motor shaft and bearing, so that the shaft does not come in direct contact with the sump oil. The bearing includes one or more axially or laterally restrained annular oil rings that capture the motor shaft journal within its inner cylindrical surface. The oil ring is in direct contact with the motor shaft journal at the ring's approximately 12 o'clock upper position. The lower portion of the oil ring proximal its 6 o'clock lower position is dipped into the oil within the sump. Often the oil ring has a grooved or otherwise textured surface to enhance friction contact with the shaft journal. Motor shaft rotation imparts oil ring rotation. As the oil ring rotates, it carries and transports an oil film on its surface from the sump oil and deposits the oil into the bearing as the previously dipped portion rotates from its prior 6 o'clock position to a new 12 o'clock position in contact with the shaft journal.
An oil ring's oil transfer rate from the sump to the shaft journal bearing is a function of and proportional to shaft rotation speed. Under low RPM, high load conditions the oil rings may not be able to maintain a desired oil transfer rate from the sump to the bearing. Conversely under high RPM conditions, oil may be slung off the ring due to centrifugal forces before a sufficient quantity can reach the bearing during the rotational trip from sump to bearing.
Additional oil ring oil transfer rate challenges are posed by induction motors that operate in non-stationary, relative motion environments, such as in marine vessels, locomotives, cranes and mining drag lines. In such applications the oil sump often is not maintained in a level condition so that the sump fluid level is at optimal height relative to the oil ring, bearing and shaft. When a motor is caused to roll, pitch or yaw relative to horizontal the oil ring may no longer be in contact with sump oil, because the oil flows to assume a new horizontal position within the motor housing.
Thus, a need exists in the art for a hydrodynamic bearing oil ring lubrication system that provides a desired oil transfer flow rate from the oil sump to the bearing that is not dependent on motor shaft rotation speed or orientation of the oil level in the sump relative to the oil ring.
One common past solution for these needs has been to dispose of the oil ring lubrication system entirely and substitute pressurized oil transport galleries in the motor housing and bearing housings that directly feed pressurized oil to the bearings, often with external oil sumps and pumps. Such solutions add manufacturing and maintenance costs to the motor that may be unacceptable in some applications. Additional bearing oil galleries and external sump systems are not easily reconfigured in presently manufactured induction motor designs that already incorporate oil rings and they are not easily retrofitted in the field or shop for motors already in operation.
In the past other oil delivery solutions have been used for hydrodynamic journal bearings in general, but they are not suitable for application to induction motors. Capillary tubes, employing sumps located above the bearing have been used to replenish bearing oil, but the sump must be refilled as it empties: by hand maintenance or through an auxiliary pump. Gravity fed capillary tubes may not be suitable for application in moving vehicles as their sumps may not always be oriented above the bearing.
Journal boxes incorporating oil-soaked felt, rock wool or the like, alone or in combination with capillary tubes have been utilized in the past in axle bearings of railroad vehicles and the like, but as with capillary tubes they are not readily suitable for application in moving vehicle induction motors. Journal boxes are unlikely to maintain oil delivery flow rates required by electric induction motors and other electrodynamic machines.
Another known oil delivery system for combined hydrodynamic/hydrostatic bearings is set forth in U.S. Pat. No. 3,720,288 as a lubrication solution for open bearing journal construction in large grinding mills. The '288 patent states that oil may be discharged directly on the exposed trunnion journal with an overhead delivery pipe supplied by an external sump and low pressure pump when the grinding mill is in normal operating mode. The lubrication system switched to pressurized hydrostatic bearing mode when the crusher transitioned to start or stop cycles. Such an oil delivery system as shown in the '288 patent is not readily applicable to a closed housing induction motor, nor would one skilled in the art today encourage potential open, unrestrained discharge of oil into the environment.